Oxybaphus nyctagineus or Mirabilis nyctaginea
(Heartleaf Four-o`clock)
Lowers leaves of Heartleaf Four-o'clock are glabrous (hairless) and have petioles 1 cm long or longer. Flowers of Heartleaf Four-o'clock drop their petals after a short period of blooming. Plants are often seen with just the calyx remaining, as in the last two photos.

Compare to Hairy Four-o'clock (Mirabilis hirsuta) , which has pubescent leaves with no petioles. Stems of Hairy Four-o'clock are also pubescent. Some references suggest that M. hirsuta and M. nyctaginea might hybridize.

Compare to Narrowleaf Four-o'clock (Mirabilis linearis), which has narrow, linear leaves.

Vegetation zone:  Plains
Time of bloom:  June - August
Origin:  Native
Eastern Colorado Wildflowers